1. Field of the Invention
The present invention relates to a variable magnification optical system, and more particularly, to a variable magnification optical system having an image stabilizing function, which is suitable for use in a video camera, a silver-halide camera, an electronic still camera, a digital camera, etc., and which is capable of stabilizing a photographed image by moving a lens unit that is a part of the variable magnification optical system in such a way as to have a component having directions perpendicular to an optical axis to optically correct shaking of the photographed image obtained when the variable magnification optical system vibrates (tilts), so as to obtain a stationary image.
2. Description of Related Art
When a photographing operation is performed from the place on a moving body, such as a running car or a flying airplane, the vibration of the moving body is propagated to a photographing system, thereby causing the so-called image shake in which shaking occurs in a photographed image.
Heretofore, there have been proposed a variety of image-stabilizing optical systems having the function of preventing shaking of a photographed image.
For example, in an image-stabilizing optical system disclosed in Japanese Laid-Open Patent Application No. Sho 56-21133, in response to an output signal of a detection means for detecting the vibration state of the optical system, an optical member that is a part of the optical system is moved in such a direction as to cancel the vibratory displacement of an image due to the vibration of the optical system, thereby stabilizing an image. In a photographic system disclosed in Japanese Laid-Open Patent Application No. Sho 61-223819 (corresponding to U.S. Pat. No. 4,927,250), in which a variable angle prism is disposed on the most object side, the apex angle of the variable angle prism is varied in correspondence with the vibration of the photographic system, thereby stabilizing an image.
In photographic systems disclosed in Japanese Laid-Open Patent Application No. Hei 1-116619 (corresponding to U.S. Pat. No. 5,270,857) and Japanese Laid-Open Patent Application No. Hei 2-124521 (corresponding to U.S. Pat. No. 5,039,211), the vibration of the photographic system is detected by utilizing an acceleration sensor or the like, and, in response to an output signal of the acceleration sensor or the like, a lens unit that is a part of the photographic system is vibrated in directions perpendicular to an optical axis, thereby obtaining a stationary image.
In addition, in a variable magnification optical system disclosed in Japanese Laid-Open Patent Application No. Hei 7-128619, which has the four-unit structure having positive, negative positive and positive lens units, the third lens unit being composed of two, positive and negative, lens subunits, the positive lens subunits of the third lens unit is vibrated to stabilize an image, i.e., to obtain a stationary image.
Further, in a variable magnification optical system disclosed in Japanese Laid-Open Patent Application No. Hei 7-199124 (corresponding to U.S. Pat. No. 5,585,966), which has the four-unit structure having positive, negative, positive and positive lens units, the whole third lens unit is vibrated to stabilize an image.
Meanwhile, in a variable magnification optical system disclosed in Japanese Laid-Open Patent Application No. Hei 5-60974, which has the four-unit structure having positive, negative, positive and positive lens units, the third lens unit is constructed into the telephoto type composed of a positive lens and a negative lens of meniscus form, thereby shortening the total length of entire optical system.
In general, according to a method in which an image-stabilizing optical system is disposed in front of a photographic system and a movable lens that is a part of the image-stabilizing optical system is vibrated to prevent shaking of a photographed image to obtain a stationary image, there is a problem that the whole apparatus including the image-stabilizing optical system and the photographic system becomes large in size and a moving mechanism for moving the movable lens becomes complicated.
Further, in an optical system in which image stabilization is performed by utilizing a variable angle prism, the amount of occurrence of decentering lateral chromatic aberration sometimes becomes large, in particular, on the long focal length side during the image stabilization.
On the other hand, in an optical system in which image stabilization is performed by parallel-decentering a lens that is a part of a photographic system in directions perpendicular to an optical axis, although there is an advantage that any additional optical system for image stabilization is not necessary, there is also a problem that a space for moving the movable lens is required and the amount of occurrence of decentering aberration during the image stabilization becomes large.
Further, in a case where image stabilization is performed by moving, in directions perpendicular to an optical axis, the whole third lens unit of a variable magnification optical system having the four-unit structure composed of four, positive, negative, positive and positive lens units, when the third lens unit is constructed into the telephoto type composed of a positive lens and a negative lens of meniscus form, there is a problem that decentering aberration, such as decentering coma or decentering curvature of field, occurs to deteriorate the image quality.
Further, optical systems each having a zoom ratio of 8 or more among the above-mentioned optical systems, although being adaptable for video cameras or the like, are insufficient for being used with electronic still cameras each having 1,000,000 pixels or thereabout, in terms of aberration correction.
It is an object of the invention to provide a variable magnification optical system having an image stabilizing function, in which a relatively small-sized and light-weight lens unit that is a part of the variable magnification optical system is moved in such a way as to have a component having directions perpendicular to an optical axis to displace an image formed by the variable magnification optical system, thereby correcting an image shake occurring when the vibration optical system vibrates (tilts), and the construction of the lens unit for correcting an image shake is appropriately set, so that decentering aberration occurring when the lens unit is decentered is corrected well while the reduction in size of the whole apparatus, the simplification of a mechanism and the lowering of load of a driving means are attempted, and, in particular, the variable magnification optical system is adaptable for electronic still cameras each having 1,000,000 pixels or more.
To attain the above object, in accordance with an aspect of the invention, there is provided a variable magnification optical system comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move along an optical axis during variation of magnification, the second lens unit comprising, in order from the object side to the image side, a first lens (L21) of negative refractive power and of meniscus form having a concave surface facing the image side, a second lens (L22) of negative refractive power, a third lens (L23) of positive refractive power and a fourth lens (L24) of negative refractive power, a third lens unit of positive refractive power, at least a part of the third lens unit being moved in such a way as to have a component perpendicular to the optical axis to displace an image formed by the variable magnification optical system, and a fourth lens unit of positive refractive power arranged to move along the optical axis during the variation of magnification, wherein the following condition is satisfied:
0.05 less than |f2/ft| less than 0.07
where ft is a focal length of the variable magnification optical system in a telephoto end, and f2 is a focal length of the second lens unit.
In accordance with another aspect of the invention, there is provided a variable magnification optical system comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move along an optical axis during variation of magnification, a third lens unit of positive refractive power, at least a part of the third lens unit being moved in such a way as to have a component perpendicular to the optical axis to displace an image formed by the variable magnification optical system, and a fourth lens unit of positive refractive power arranged to move along the optical axis during the variation of magnification, wherein the following condition is satisfied:
0.42 less than |LS/ft| less than 0.59
where LS is a distance from a lens surface located on the most object side of the variable magnification optical system to a lens surface located on the most object side of the third lens unit, and ft is a focal length of the variable magnification optical system in a telephoto end.
In accordance with a further aspect of the invention, there is provided a variable magnification optical system comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move along an optical axis during variation of magnification, a third lens unit of positive refractive power, at least a part of the third lens unit being moved in such a way as to have a component perpendicular to the optical axis to displace an image formed by the variable magnification optical system, the third lens unit comprising, in order from the object side to the image side, a first lens (L31) of positive refractive power having a convex surface facing the object side, a second lens (L32) of negative refractive power and of meniscus form having a concave surface facing the image side, and a third lens (L33) of positive refractive power, and a fourth lens unit of positive refractive power arranged to move along the optical axis during the variation of magnification, the fourth lens unit comprising a positive lens and a negative lens.
In accordance with a still further aspect of the invention, there is provided a variable magnification optical system comprising, in order from an object side to an image side, a first lens unit of positive refractive power arranged to move along an optical axis during variation of magnification, the first lens unit having, on the most object side thereof, a negative lens of meniscus form having a concave surface facing the image side, a second lens unit of negative refractive power arranged to move along the optical axis during the variation of magnification, the second lens unit having, on the most object side thereof, a negative lens of meniscus form having a concave surface facing the image side, a third lens unit of positive refractive power, at least a part of the third lens unit being moved in such a way as to have a component perpendicular to the optical axis to displace an image formed by the variable magnification optical system, and a fourth lens unit of positive refractive power arranged to move along the optical axis during the variation of magnification, wherein the following condition is satisfied:
0.5 less than |m1/m2| less than 2.5
where m1 and m2 are amounts of movement of the first lens unit and the second lens unit, respectively, required for the variation of magnification from a wide-angle end to a telephoto end.
In accordance with a still further aspect of the invention, there is provided a variable magnification optical system comprising, in order from an object side to an image side, a first lens unit of positive refractive power arranged to move along an optical axis during variation of magnification, a second lens unit of negative refractive power arranged to move along the optical axis during the variation of magnification, an aperture stop arranged to move along the optical axis during the variation of magnification, the aperture stop varying an aperture thereof to adjust an amount of passing light, and the aperture stop being located nearer to the object side in a wide-angle end than in a telephoto end, a third lens unit of positive refractive power, at least a part of the third lens unit being moved in such a way as to have a component perpendicular to the optical axis to displace an image formed by the variable magnification optical system, and a fourth lens unit of positive refractive power arranged to move along the optical axis during the variation of magnification, wherein the following condition is satisfied:
xe2x80x830.5 less than |m1/m2| less than 2.5
where m1 and m2 are amounts of movement of the first Lens unit and the second lens unit, respectively, required for the variation of magnification from the wide-angle end to the telephoto end.
In accordance with a still further aspect of the invention, there is provided a camera comprising, as a photographic lens, a variable magnification optical system according to any one of the above aspects.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.